Ureteral blockage is a serious and very painful affliction and can result in death if not promptly and effectively treated. The blockage can occur for a number of reasons including the passage of kidney stones or debris from such stones into the ureter where they become entrapped, tumors growing against the outer wall of the ureter and forcing constriction and internal or ureter wall tumors. Eventually the problem is solved by surgery, medication or waiting until debris is naturally cleared from the ureter. However, a stent must often be inserted in the ureter on a temporary basis to provide drainage until the condition can be corrected.
There are many different ureteral stents available. The main function of each of these ureteral stents is to bypass ureteral obstruction and to provide urinary drainage from the kidney to the bladder for a period of time which varies but is usually of the order of a few days to several months.
There are several methods of stent placement within the ureter. One method involves passing a guide wire up the ureter into the kidney. Thereafter, a tubular stent is fed and coaxially slid up the guide wire into the ureter using a tubular stent pusher. An alternate method employs placing a tubular stent having a closed or partially tapered shut proximal end over a guide wire. The stent is thereafter advanced up into the ureter by pushing the guide wire against the closed or partially tapered shut end. Another alternate method is to place the tubular stent over the guide wire with the stent pusher over and affixed to the guide wire behind the stent and thereafter to advance the entire assemblage into the ureter. These methods can also be used, with appropriate surgery to provide access, to insert a stent from the kidney downwardly through the ureter to the bladder.
Early ureteral stents were straight. As a result, after placement into the ureter, these straight stents often migrated or were expelled from the ureter as a result of peristaltic action by the ureter. Later ureteral stents, therefore, have been designed with means of retention on one or both ends of the stent. The retention means is intended to inhibit stent migration either upward into the kidney or downward into the bladder. Retention means that have been employed are in the form of hooks, pigtails, coils, corkscrews, malecots or any other practical shape that will serve the purpose.
Ureteral stents also come in many different lengths. The variations in stent length are often necessary to accommodate the different ureter sizes in different size patients. As a result, a stock of different length ureteral stents must often be kept available. To overcome this problem of stocking many different length ureteral stents, some stents have been designed in the form of an expanding coil or corkscrew as disclosed in U.S. Pat. Nos. 4,531,933; 4,643,716; 4,671,795; and 4,813,925, or utilize connectors as disclosed in U.S. Pat. No. 4,790,810.
In addition to varying lengths, ureteral stents are also made with varying diameters, e.g., from 4.5 French (0.059") to 8.5 French (0.112"), and varying degrees of hardness. Ureteral stents with smaller diameters are usually easier to insert but may not provide sufficient drainage, whereas stents with larger diameters allow for increasing drainage capacity through the ureter but may be difficult to insert. Stiff ureteral stents are also easier to insert than are softer stents, but once inserted can lead to increased patient discomfort. Softer stents, on the other hand, provide more comfort for the patient but are more difficult to insert due to their softness. Presently, most available stents are either made of silicone as disclosed in U.S. Pat. No. 4,212,304 or of a harder polymer. Silicone may increase patient comfort, but because of the softness of silicone, it is more difficult to guide the stent into the ureter. Once in the ureter, the softness of the silicone increases the likelihood of migration of the stent because rigid retention means are not available.
To balance ease of insertion, better retention and patient comfort, some ureteral stents have been designed combining a stiff material at the kidney end for easier insertion and better retention with a softer material at the bladder end for patient comfort. These dual hardness stents are disclosed in U.S. Pat. Nos. 4,820,262; 4,874,360; and 4,931,037.
It is at times desirable or necessary to provide a stent which is wider at one end, either its proximal end or its distal end, perhaps as much as 16 French in diameter, and narrower at the other end, perhaps 4.5 French to 7 French. In the past, this has usually required insertion from the proximal (kidney) end of the ureter, a relatively difficult procedure.
Swellable ureteral stents utilizing hydrophilic polymers of the nature set forth in U.S. Pat. No. 4,377,010 and elsewhere, generally as coatings on other materials but also alone, have been investigated using piglets (See An Experimental Study of Hydrophilic Plastics for Urological Use, J. W. A. Ramsey, et al, British Journal of Urology, Volume 58, pp 70-74, 1986 and/or Evaluation of Polymeric Materials for Endourologic Devices, H. K. Mardis, Seminars in Interventional Radiology, Volume 4, Number 1, pp 36-45, March 1987) but have not received acceptance in the medical community. They have exhibited high biocompatibility. Such stents have not been formulated with different softnesses and/or swellability at different portions thereof whereby optimal comfort combined with retainability, ease of insertion and the ability to provide stents which will assume specially desired shapes on hydrating have not been available or contemplated.
Although ureteral stents have been designed to address one or more of the above problems specifically, there are currently no ureteral stents incorporating features that can bypass all of the aforementioned disadvantages. It is thus desirable to have a ureteral stent that inserts easily, can provide selectable and different degrees of softening and/or swelling on different portions of the stent, can have a tapered tip that expands, has an adequately large size once expanded, provides strong retention, can be inserted into the ureter yet can, if desired, have a significantly larger diameter at the distal and/or the proximal end upon hydration and at the same time increases patient comfort.